The present invention relates to a load current control device, and more particularly to a load current control device for controlling the magnitude of a current flowing in a solenoidal load.
Power steering systems which can easily effect steering of automobiles by using steering assistance are put into practice. In such steering systems, information related to steering every moment is detected by a detector attached on a steering wheel etc. to change this information into an electric signal to transmit the electric signal to a steering mechanism for actually carrying out steering operation by way of an electric wire. The steering mechanism is operated by an oil pressure system. By controlling an oil flow of the oil pressure system, its output is controlled. The oil flow is controlled by the opening and closing operation of a solenoid valve. The opening and closing operation of the solenoid valve is controlled by the magnitude of a current flowing in a solenoid. The control of the magnitude of a current flowing in the solenoid is effected by turning on and off a power delivered to the solenoid in accordance with a duty factor determined based on the above-mentioned steering information signal.
However, the drawback with the conventional power steering system is that even when the power supplied is turned on and off in accordance with a predetermined duty factor, voltage of the power source varies and the resistance value of the solenoid varies due to changes in temperature based on changes in the condition of the solenoid valve, with the result that the magnitude of a current also varies.
In addition, a detection circuit for detecting breaks or shorts of the solenoid is provided separately from a control circuit for a current flowing in the solenoid.